This is not a difficult achievement, but it's going to take a lot of time.
It's mostly similar in strategy to the other two landslide achievements:
As you collect vote coins, your starting votes and your vote multipliers will increase, allowing you to get landslide victories faster. Depending on how often you check in on the game, you can get multiple landslides per (real-world) day. You do this by getting ~320 million votes before the current campaign ends, giving you the option to accept an early landslide. This cuts the campaign short and starts a new one.
I usually check in on the game 2-3 times a day (before work, after work, and before bed), but in theory you could check every 2 hours to restart the double votes upgrade and buy more building upgrades. Note that you need to have ~320 million votes on hand to be able to get a landslide, you can't get it if you have 500 million votes but have spent 400 million of those on upgrades.
At the rate of 2 landslides per day, this will take 50 days. If you play more intensely, it's possible you could do it in a month.